Movatterモバイル変換

[0]ホーム
URL:

Skip to content

Navigation Menu

Sign in
Appearance settings

Search code, repositories, users, issues, pull requests...

Provide feedback

We read every piece of feedback, and take your input very seriously.

Saved searches

Use saved searches to filter your results more quickly

 Sign up
Appearance settings

Commitf658235

Browse files
author
Amit Kapila
committed
Prohibit pushing subqueries containing window function calculation to
workers.Allowing window function calculation in workers leads to inconsistentresults because if the input row ordering is not fully deterministic, theoutput of window functions might vary across workers. The fix is to treatthem as parallel-restricted.In the passing, improve the coding pattern in max_parallel_hazard_walkerso that it has a chain of mutually-exclusive if ... else if ... else if... else if ... IsA tests.Reported-by: Marko TiikkajaBug: 15324Author: Amit KapilaReviewed-by: Tom LaneBackpatch-through: 9.6Discussion:https://postgr.es/m/CAL9smLAnfPJCDUUG4ckX2iznj53V7VSMsYefzZieN93YxTNOcw@mail.gmail.com
1 parentd8030c6 commitf658235

File tree

3 files changed

+42
-0
lines changed

3 files changed

+42
-0
lines changed

‎src/backend/optimizer/util/clauses.c

Lines changed: 14 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -1161,6 +1161,20 @@ has_parallel_hazard_walker(Node *node, has_parallel_hazard_arg *context)
11611161
return true;
11621162
}
11631163

1164+
/*
1165+
* Treat window functions as parallel-restricted because we aren't sure
1166+
* whether the input row ordering is fully deterministic, and the output
1167+
* of window functions might vary across workers if not. (In some cases,
1168+
* like where the window frame orders by a primary key, we could relax
1169+
* this restriction. But it doesn't currently seem worth expending extra
1170+
* effort to do so.)
1171+
*/
1172+
elseif (IsA(node,WindowFunc))
1173+
{
1174+
if (!context->allow_restricted)
1175+
return true;
1176+
}
1177+
11641178
/*
11651179
* As a notational convenience for callers, look through RestrictInfo.
11661180
*/

‎src/test/regress/expected/select_parallel.out

Lines changed: 23 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -182,6 +182,29 @@ select count(*) from tenk1;
182182
(1 row)
183183

184184
reset role;
185+
-- Window function calculation can't be pushed to workers.
186+
explain (costs off, verbose)
187+
select count(*) from tenk1 a where (unique1, two) in
188+
(select unique1, row_number() over() from tenk1 b);
189+
QUERY PLAN
190+
------------------------------------------------------------------------------------
191+
Aggregate
192+
Output: count(*)
193+
-> Hash Semi Join
194+
Hash Cond: ((a.unique1 = b.unique1) AND (a.two = (row_number() OVER (?))))
195+
-> Gather
196+
Output: a.unique1, a.two
197+
Workers Planned: 4
198+
-> Parallel Seq Scan on public.tenk1 a
199+
Output: a.unique1, a.two
200+
-> Hash
201+
Output: b.unique1, (row_number() OVER (?))
202+
-> WindowAgg
203+
Output: b.unique1, row_number() OVER (?)
204+
-> Index Only Scan using tenk1_unique1 on public.tenk1 b
205+
Output: b.unique1
206+
(15 rows)
207+
185208
explain (costs off)
186209
select stringu1::int2 from tenk1 where unique1 = 1;
187210
QUERY PLAN

‎src/test/regress/sql/select_parallel.sql

Lines changed: 5 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -83,6 +83,11 @@ drop role regress_parallel_worker;
8383
selectcount(*)from tenk1;
8484
reset role;
8585

86+
-- Window function calculation can't be pushed to workers.
87+
explain (costs off, verbose)
88+
selectcount(*)from tenk1 awhere (unique1, two)in
89+
(select unique1, row_number() over()from tenk1 b);
90+
8691
explain (costs off)
8792
select stringu1::int2from tenk1where unique1=1;
8893

0 commit comments

Comments
 (0)
[8]ページ先頭
©2009-2025 Movatter.jp